“She’s not wearing that dress, the dress is wearing her,” the fashion police might grumble before making an arrest. “London Boulevard” commits a similar crime – it’s a movie that ultimately overpowers its director.

That said, there is much to admire in this work from William Monahan, who directed and wrote the script from a novel by Ken Bruen. Monahan, having won the Oscar for “The Departed,” is completely in his element with noir scripts, setting up compelling narrative threads and knocking out smart, fast, sometimes-funny lines.

Colin Farrell plays Mitchel, an ex-con determined not to return to jail. But, in need of quick cash, he hooks up with simple-minded Billy (Ben Chaplin) and helps him make his rounds collecting money in South London for flashy gangster boss Rob Gant (Ray Winstone). At a pub gathering to celebrate Mitchel’s release, a pretty girl (Ophelia Lovibond) tells him he could approach a “retired” friend of hers for a job as a handyman.

The friend turns out to be anxious and vulnerable Charlotte (Keira Knightley), a famous actress who can’t leave her Holland Park home without being bombarded by the snapping and flashing of verminlike paparazzi. He catches her eye (Colin Farrell just has a way of doing that), then earns her trust as well as that of her manager, Jordan (David Thewlis), a former actor and fluent drug-taker. At the same time, Mitchel tends to his unstable sister (Anna Friel) and seeks retribution for the murder of a damaged old criminal (Alan Williams).

Still, the ties with the underworld are tough to break. After Mitchel endures a beating from rival thugs (Billy flees), the boss offers him a promotion. “No thanks, got a new job” does not go over well and Mitchel has to find a way to extricate himself from Rob.

“London Boulevard” has many of the elements of a first-rate neo noir. It starts with high energy (the music helps) and an exciting pace – Monahan seems in command of his material. Chock full of dodgy characters, the movie is nicely cast and all the actors are interesting to watch. Farrell and Knightley have a spindly spark of chemistry, which is about all you could expect from this ships-in-the-night liaison.

But, about two thirds of the way though, the movie’s rhythm goes haywire, lingering too long on one storyline, then rushing abruptly to another. It’s hard not to notice the drafty holes in the story as it shunts to its slightly surprising, yet far from inevitable, conclusion.

Flaws aside, however, “London Boulevard” is an entertaining yarn with a considerable amount of visual flair (Chris Menges shot it) and intelligence. So the movie police might complain – film noir with Farrell and Knightley is still a little bit of all right.